Field
The instant disclosure relates to steganography, and in particular to methods and systems for protecting data using steganography.
Description of the Related Art
In today's world, communication security is crucial for the confidentiality of data being transmitted. Currently, more and more data is being transmitted with the help of devices, such as computers, using the Internet and other means as the communication channels. With technological advancement in data communications, unauthorized access to electronic data also has increased, Thus, there is a need to develop new ways to counter unauthorized access to data.
There are two widely used methods for protecting electronic data: cryptography and steganography. Cryptography is a technique for converting data into some unintelligible form that can be decoded only by the intended recipients. In cryptography, a sender encrypts a message using some algorithm, with the help of a key, which is shared with a receiver prior to the communication of the encrypted message to the receiver. The receiver can then decode the message using the same algorithm and the key.
Steganography is a method of hiding data in a carrier object in such a way that the existence of the data being sent is concealed. The carrier object can be any suitable carrier object, such as a text file, an image, a video file or an audio file. In image steganography, the carrier object typically is a digital image. This type of carrier object typically is called a cover image. Data typically is embedded in binary form either in the spatial domain or in the frequency domain of the cover image to produce a steganographic (or stego) image. A receiver can extract the embedded data using a predefined extraction algorithm. Alternatively, a key used by the sender to embed the data can be shared with the receiver prior to the stego image transmission to the receiver, and used by the receiver to extract the embedded data.
In the spatial domain, data is embedded directly into pixel values of the cover image. In the frequency domain, the cover image first is transformed into its frequency domain, and then data is embedded into the frequency coefficients. The cover image can be binary, a gray-level image or a color image.
There are various conventional stegnography techniques available in both the domains. In the spatial domain, there are pixel value differencing techniques and side matching techniques. In the frequency domain, there are LSB (least significant bit) substitution techniques and techniques using secret keys. The most widely used stegnography techniques involve LSB substitution in an image.
There are three basic elements in a typical steganography method. These elements are imperceptibility, capacity and robustness. Imperceptibility involves the stego image and the cover image not being distinguishable from each other. Capacity refers to the maximum amount of data that can be embedded in a cover image without producing significant distortion in the stego image. Robustness refers to the resistance capability of the method against various steganalysis attacks.
Because there typically is a trade-off between imperceptibility, capacity and robustness, there is a need to improve imperceptibility and robustness in steganography methods.